Fluid pumping and separation apparatus

ABSTRACT

Pumping apparatus is provided for separating liquids from solids in a mixture thereof, the apparatus preferably being of the peristaltic type with a cage with rollers circumferentially spaced around its periphery rotable within a casing, there being at least two flexible tubes extending around the cage, a first, evacuation tube having an inlet end held open within the casing and an opposite end connected to a first outlet in the casing and a second pumping tube extending between an inlet in the casing adapted to be connected to a liquid to be pumped and a second outlet from the casing, whereby upon rotation of the cage, e.g. by an electric motor, a negative pressure will be generated within the casing and the liquid will be pumped through the apparatus. For separating solids suspended in/mixed with the mixture being pumped, an electrical or electrostatic charge is introduced into the mixture. To prevent the tubes from wandering laterally and becoming worn within the casing, a plurality of guide spools is located on the cage, preferably circumferentially alternating with the rollers on the cage. The electrical or electrostatic charge within the mixture may be generated using electrodes and a low voltage AC current, or with polypropylene brushes, or strands or polypropylene located in a pumping tube.

[0001] This is a continuation/division of the International Application No. PCT/GB99/0703 with an International filing date of Nov. 8, 1999, now abandoned.

[0002] The present invention relates to an apparatus for and method of pumping fluids and more particularly, an apparatus for and method of separating liquids from solids in a mixture of liquids and solids. The method and apparatus can be used for the processing of waste water or waste liquids carrying solids or particulate matter in any proportion. For example, the invention can be used for the dewatering of animal slurries, sewage slurries and for the treatment of liquid effluent from a vegetable washing plant, from a mushroom farm, or for the treatment of the liquid effluent from pultry packing plants, dairies, creameries and chese making factories. It can also be used for treating industrial, municipal and commercial waste liquids, municipal sewage sludges, including digested and non-digested primary and secondary sludge, industrial sludges such as paper and the like.

[0003] Furthermore, the invention can be used for the extraction of juices from citrus friuts and other fruit products, such as current and apple pulp, or even for separating the juice and fruit flesh from pips, stalk, branches, and leaves during the harvesting of grapes, blackcurrants and the like.

[0004] The invention makes use of known peristalic pumping pricipals. In DE-A-2234592, and US-A-5281112, a peristaltic pump is used to separate solids from liquids. In these specifications, an external vacuum source is used to generate a reduced pressure within the peristaltic pumping chamber. Alternative constructions of peristaltic pumping apparatus are disclosed in EP-A-0470333 and JP 61016282.

[0005] In our earlier patent specification, WO 966/31269, a peristaltic fluid pumping or sludge separation devise id disclosed. In this device, at least two lay-flat tubes are entrained around plurality of rollers supported on a roller cage and rotable within a sealed casing. One of the lay-flat tubes is used to generate a reduced pressure within the casing and the other tube is used for pumping a fluid mixture of liquids and solids. The liquids are separated from the solids in this apparatus by using a composite lay-flat tube for the separation process, the composite lay-flat tube having a tapered filter tube therein through which the mixture to be separated is forced. The present invention is an improvement over the apparatus and method disclosed in WO 96/31269.

[0006] According to the broadest aspect of the present invention, we provide a pumping apparatus for separating solids from liquids in a fluid mixture of solids and liquid, comprising a pump for pumping the fluid mixture from a supply thereof through a pipe into a settling tank, means to introduce an electrical charge into the fluid mixture whereby solids will precipitate from the fluid mixture in the settling tank. Preferably there is a liquid outlet towads the top of the settling tank, and a solids outlet towards the bottom of the settling tank.

[0007] More particularly, we provide peristaltic pumping apparatus comprising at least two flexible deformable tubes entrained around a cage, rotable within a part acurate casing and supporting a plurality of rollers which push through the tubes by squeezing the tubes, a first one of the tubes having a first end held open to the interior of the casing and an opposite end connected to a first outlet from the casing, whereby, upon operation of the apparatus, a pressuer (herein called negative pressuer) which is less than that surrounding the casing will be generated within the casing, a second one of the tubes being connected at one end to an inlet in the casing, adapted to be connected to a fluid mixture of solids and liquids to be pumped and its opposite end being connected to a second outlet therein, whereby upon operation of the apparatus, the negative pressuer will cause the second tube to move from a flattened state to a tubular state, whereby the fluid will be pumped through the second tube to the outlet, a settling tank, a pipe connecting the settling tank to the second outlet and means ti introduce an electrical charge into the fluid mixture whereby solids will precipitate from the fluid mixture in the settling tank.

[0008] Filtering means may be located at or adjacent the outlet end of the second tube so that as the fluid is pumped through the tube, solids will be separated from liquids within the fluid. The filtering means may comprise a flexible sleeve, which may be formed of textle material, at the outlet of the tube, one end of the sleeve being connected to the tube and the opposite end being connected to an outlet pipe of the filtering means, the sleeve being located within a casing having a liquid outlet therein through which filtered liquids can pass. The sleeve may be tapered construction so that its outley end is reduced cross-sectional area, relative to its inlet end.

[0009] Also according to the present invention, we provide an apparatus for separating solids from liquids in a mixture of solids and liquids comprising a closed casing having a side wall, at least part of which is acurate, and a pair of spaced opposed end walls, connected by said part acurate side wall, a cage rotatable within the casing, the cage having rollers spaced around its periphery, and a first resilient tube extending around the cage and located between the peripheries of the rollers and the internal surface of the accurate side wall, one end of the first tube being connected to a first outlet of the casing and the opposite end of the tube being connected to means within the casing to hold open said end of the tube, there being a non-return valve located within, or at the end outlet end of, the first tube, means to cause rotation of the cage such that air within the casing will be drawn into the held-open end of the tube and pumped along the tube in peristaltic manner to the outlet, the non-return valve preventing air from re-entering the tube, whereby the pressure within the casing is reduced, relative to that around the casing, at least one further resiliently deformable tube entrained over at least some of the rollers of the cage, so as to extend between the rollers and the acurate part of the side wall of the casing, one end of said further tube being connected to a second outlet in a wall of the casing and the opposite end thereof being connected to an inlet in a wall of the casing, said inlet being adapted to be connected to said mixture, whereby rotation of the cage not only reduces the pressure within the casing to cause the at least one further tube to expand into a tubular state, but also pushes said mixture to be pumped along the further tube from the inlet to the outlet, and means to separate liquid from solids in said mixture, said means comprises means for generating an electrical or electrostatic charge, which causes separation of solids from liquid mixture, e.g. by causing flocculation of the solid. In another arrangement, both means generate an electrical charge or an electrostatic charge and filtering may be provided.

[0010] The filtering means may comprise a perforated tubular member secured to the outlet end of the further tube, the perforated member preferably being flexible and formed of textile material and preferably tapering from its inlet end to its outlet end, the outlet end being connected to an outlet pipe in a filter casing, and there being a liquid in said casing for liquids separated from said mixture. Alternatively, the filtering means may be a sieve-like filter sleeve located within said at least one further resiliently defotmable tube, and incorporate at least two electrodes therein, or on the surface of the sleeve, and the other running centrally of the sleeve, each extending the full length of the sleeve.

[0011] Also according ta the present invention, we provide a method of pumping peristaltically and a method of separating solids perstaltically from liquids in a mixture of solids and liquids, including the steps of locating a pair of flexible tubes within a casing having an at least part arcuate side wall, entraining the tubes around a cage having a plurality of rollers supported thereon, whereupon the flexible tubes are located between some of the rollers and the part side wall, one of said tubes being an evacuatiug tube and the other being a pumping tube, connecting an inlet end of the evacuating tube to means to hold open that end of the tube and providing a non-return valve for said tube, causing rotation of the cage within the casig to generate a reduced pressre, relative to external pressure, within the casing, and connecting an inlet end of the further tube to an inlet in the casing, which inlet is adpted to be connected to a mixture to be pumped, whereby the reduced pressure will cause said mixture to be drawn into the further tube and then be pumped through the further tube and out of the casing, and providing means to cause solids in said mixture to be separated from solids therein, said means comprises means to generate an electrical or electrostatic charge in the mixture.

[0012] Preferably, in order to prevent wear and tear of the tubes entrained around the rollers on the cage and to prevent the tubes from moving laterally along the rollers within the casing, the cage supports a plurality of guide spools for the respective tubes. Preferably there are a plurality of shafts circumferenially spaced around the cage, alternate shafts being used to support the rollers and the guide spools for the tubes.

[0013] In a prefered arrangement, an evacuating tube is located with the casing between a pair of pumping tubes, and hence, on each guide spool shaft, three separate guide spools are provided, a central one being for the evacuating tube and locatcd on either side thereof, there is a lateral guide spool for the respective pumping tube. Preferably, also, each roller for the tubes is divided into a central portion for the evacuating tube and spaced to either side thereof, a lateral portion for the respective pumping tube.

[0014] Several embodiments of peristaltic pumping and separating apparatus of the present invetion are now described by way of example with reference to the accompanying dawings in which:

[0015]FIG. 1: is a side elevation of one embodiment of a portable pump/separator,

[0016]FIG. 2 is a plan view of the pump/separator,

[0017]FIG. 3: is a front elevation of the pump/separator,

[0018]FIG. 4: is a scrap plan view looking in the directon of the arrow A in FIG. 1,

[0019]FIG. 5: is a side elevation showing a rotor drum which is located within the casing of the pump/separator shown in FIGS. 1 to 4.,

[0020]FIG. 6: is the section on the line IX-IX shown in FIG. 5,

[0021]FIG. 7 is the section on the line X-X in FIG. 5,

[0022]FIG. 8 is the schematic view of an alternate embodiment of pumping and separating apparatus,

[0023]FIG. 9 is the schematic scrap view showing a rotor drum having one pumping tube entrained around it and connected to an inlet and an outlet,

[0024]FIG. 10 is the schematic view of a sludge charging tank.

[0025] Referring to FIGS. 1 to 4, the perstaltic pump/separator is a moble version having a wheeled support chassis 1 carrying an electric motor 3 driving the pump which is shown generally at 5, generally in known matter. The pump 5 has an overall casing 7 formed of sheet steel, having a part acurate side wall 9 and a pair of end walls 11, which are split as shown at 13 and support split bearing members 15 for a central drum shaft 17.

[0026] The casing 5 is braced by a stiffening frame 19. The shaft 17 supponts a drun 21 which is shown in greater detial in FIGS. 5 to 7.

[0027] The casing 5 has an upper cantilever portion 23 fitted with a removable inspection cover 24 and a lower cantilever portion 25 fitted with a removable inspection cover 26. Projecting arms 27 extend outwardly from each side of the cantilever portion 23 to support two filter chambers 29, as shown in FIG. 2. These filter chambers are optional. On the fromt wall of the upper cantilever portion 23, two tube or hose coupling members 31 are provide for a pair of pumping tubes and a further tube or hose connector 33 for an evacuation tube (to be described hereinafter). As can clearly be seen in FIGS. 1 and 2, the ends of the coupling members 31 located outside the casing 5 are connected with proprietary members to respective ones of the filter chambers 29, wheras a non-return valve 35 is mounted on the outer end of the connector 33.

[0028] As can clearly be seen from FIG. 4, the cantilever portion 25 supports two further hose coupling members 37 for theperilistic pumping hoses (not shown). Located internally of the casing 5 within the cantilever portion 25 in an evacuation hose support member 39. This is mounted on upstanding brackets supported on the base of the casing 5 and has an open end to the interior of the casing 5, as shown at 43.

[0029] As can be seen from FIGS. 5 to 7, the drum 21 has a drive shaft rotatable in the bearing members 15, supported by the end walls of the casing 5 and supported on the drive shaft 17 towards respective ends thereof are two spaced support plates 45, ahving four accurate side walls at the junctions of which are four mounting channels, each to accommodate a roller support shaft 49. To either of each mounting channel 47, a slot is provided to enable mounting plates fixed on either end of the support shaft 49 to be adjustably located in the channel 47 in known manner, using suitable fixing screws 53. Located midway along each side wall of each support plate 45 ia a further mounting channel 55 for a support shaft 56 for a plurality of tube guide spools 57 ( see FIGS. 2 and 7). The shafts 56 are located in their respective mounting channels 55 in the same manner as the shafts 49.

[0030] As a be seen more clearly in FIG. 6, each of the roller support shafts 49 rotatably supponts two pumping tube rollers 59 towards each end thereof, and a centrally located evacuatoin tube roller 61, each of the rollers 59 and 61 being provided with its own bearings and the respective rollers being separated from one another by suitable spaces 63. Whereas the pumping rollers 59 are of regular cylindrical construction, the evacuation tube roller 61 is contoured so as to have a central region with a uniform diameter, but tapered end regions, as shown at 65.

[0031] As can more clearly be seen from FIG. 7, each of the shafts 56 supports a centrally located guide spool 58 for the evacuation tube and, located to either side thereof, a guide spool 57 for the respective pumping tubes. As can be seen from FIG. 7, the two spools 57 for the pumping tubes are somewhat wider then that for the evacuation tube since in the preferred arangement, the pumping tubes are of larger diameter than the evacuation tube. Each of the spools is provided with its own bearing so as to be able to rotate freely on its respective support shaft 56.

[0032] An inlet end of a resiliently deformable evacuation tube or hose 71 is connected in fluid tight miner using a screw connector 73 to the hose support member 39 an the hose 71 is then entrained around respective ones of the rollers 61 and guides 58 of the drun 21 and its outlet end is then connected in fluid-tight manner to that end of the connector 33 located within the casing 5 by a screw connector 75. Likeise, an inlet end of a pumping hose or tube 77 is connected by a screw connector 79 to that end of each tube connector 39 located within the casing 5 and is then entrained around respective ones of the rollers 59 and guide spools 57, and its outlet end is then connected using a respective screw connector 81 to that end of the respective tube coupling member 31 located within the casing 5. Tension in the respective hoses can be adjusted by adjusting the radial spacing of the shafts 49 and 56 from the shaft 17 of the drum 21.

[0033] The flexible tubes 71 and 77 may either be suitably reinforced, resiliently deformable, tubular hoses which when collapsed will spring back to their tubalar form or alternatively, may be reinforced, lay-flat hosing, such as that used by fire brigades. It is preferred that The evacution hose 71 be in the form of a lay-flat hose, and the chamfered lateral portion 65 of the roller 61 are provided so as not completely to squash the two lateral edge regions of the lay-flat hose during use.

[0034] As will be apparent from FIG. 1 and FIG. 5, the pump is operated by rotatng the drum 21 clockwise. Such rotation will cause the evacuation tube 71, as each roller 61 rolls around the tube, to be squashed substantally completely flat so as to drive any air within the tube from the inlet end of the tube connected to the tube support member 39 around the tube and out of the outlet hose connector 33. The presence of the member 39 will ensure that at no time is the inlet end of the evacuation tube 71 colapsed. Because the member 39 is located wihin the casing 5 which is a totally sealed casing, each time a roller passes over the evacuton tube, a little bit more air from within the casing will be evacuated therefrom, so that eventually, the pressure within the casing 5 will be reduced substially from normal atmospheric pressure outside the casing. Because the inside of the casing is therefore, during normal operation of the pump, at a pressure substtially reduced relative to external pressure, the stiffening frame 19 for the casing is most important. AT the same time as the rollers 61 are rolling over the evacuation tube 71, partially to evacuate the interior of the casing 5, so the two other rollers 59 will be rolling over the two pumping hoses 77. Because the pressure within the casing has been reduced, the two pumping hoses will be fully inflated, ie. completely tubular, except where they are engaged by the rollers 59 (because, of couse, the interior of the pumping tubes 77 are in communication with the exterior of the casing 5 through there respective coupling members 31 and 37). If the coupling members 37 are connected outside the casing 5 to a suitable fluid to be pumped, the passage of the rollers 59 around the pumping tube 77 within the casnig will cause any fluid within the tubes 77 to be pushed around the tube 77 from their inlet ends, towards their outlet ends connected by the connectors 81 to the coupling numbers 31. This in turn will cause fluid to be drawn into the casing through the tube inlets 37 and fluid to be pumped out of the casing through the couplings 31. Because the pressure within the casing 5 is reduced relative to atmospheric pressure, the two pumping hoses 77 will always be caused to return to their fully tubular configuration, immediately after a roller 59 has rolled over the tube. Hence, using the peristaltic pumping priciples described, the pump will generate a negative pressure within the casing and at the same time, cause fluid to be pumped through the casing, through the two pumping tubes 77.

[0035] It is possible to separate liquids from solids in the fluid being pumped by the pump, by use of the two filter clambers 29. However, it is possible to dispense with these chambers altogether if the apparatus is merely to be used as a pump or alternatively, to dispense with the filters within the filter chambers, or alternatively, to use a different fiter arrangement, or to use other means to achieve this.

[0036]FIG. 8 shows an alternative construction of pumping and separaing apparatus schematically, with sludge to be pumped and separated indicated generally at 101 and the pumping and separating apparatus, which is largely identical to that shown generally at 5 in FIG. 1, shown at 105. Although a negative pressure is creaed within the apparatus 105, as in the embodiment of FIG. 1, only a single pumping tube 107 is illustrated which is entrained around some of the rollers of the drum 121. The tube 107 is corrected at an inlet end to the sludge 101 by an inlet pipe 103 and at its outlet end the tube 107 is connected to an outlet pipe 109 which deposits the sludge in a settling tank 111.

[0037] In order to impart an electrostaic charge to the sludge being pumped through the tube 107, a plurality of strands of polypropylene 113 are entrained within the tube 107. The lengths of these strands can be varied, but it is preferred that one end of the polypropylene strands is anchored to the tube 107 at their inlet ens and the other ends are allowed to “stream” out of the outlet end of the tube 107. Material other than polypropylene and which is also known to generate an electrostatic charge could be used as an alternative. In order to increase the electrical charge of the pumped sludge which is deposited in the settling tank 111, two electrodes 115 and 117, which act alternatly as a cathode and an anode, are supported above the settling tank 111, which is earthed as shown at 119. An AC current of low voltage, e.g. about 12 volts, is supplied to the electrodes 115, 117. In order to increase still further the electrical/electrostatic charge applied to the sludge within the settling tank 111, a proportion of the sludge being pumped from the apparatus 105 into the outlet line 109 is taken from the pipe 109 and into a further pipe 122, an outlet end of which discharges into a further tank 123. The tank 123 has a semi-arcuate metallic screen 125 therein, the apertures in which are approximatly 2 or 3 millimetres in diameter, and rotable within the screen 125 are a plurality of paddles supported on an axis of rotation 127, each of the paddles extending across the full width of the screen 125 and being comprised of a plurality of polypropylene bristles 129 which contact the surface of the screen 125. These bristles impart further electrostatic charge to the sludge which exits from the tank 125 through an outlet pipe 131 for dischage into the settling tank 111. The Paddles can rotate at about 7 rpm. and are preferably driven by their own motor.

[0038] There may be a plurality of rollers located between each of the bistles 129; these rollers are supported on radial arms on the shaft 127 in a similar manner to the bristles 129, and they are preferably biased into contact with the screen 125, e.g. by spring loaded arms. Both the bristles and the rollers may be segmented instead of continuous.

[0039] Instead of providing a screen 125 in the tank 123, ihe lowner semi-circular part of the tank may have a plurality of upstanding chevron shaped ribs welded or formed thereon, against which the brisles 129 (and rollers if provided) rub. This agitates the bristles (and rollts) in different directions, thus helping to generate an electrostatic charge ithin the sludge in the tank 125. The tank may be closed, circular in cross section, and may have an inlet in a top thereof, and an outlet in the base, at one end thereof, instead of the open topped, as shown in FIG. 8.

[0040] It is preferred that the tank 123, instead of being connected to the pipe 109 by the pipe 122, is provided at the outlet end of the pipe 109, before the tank 111.

[0041] The electrical or electostatic charge imparted to the sludge being pumped may be imparted just by the presence of the polypropylene strands 113, or just by the tank 123 with its bristles 129 and optional rollers, or just by providing the electrodes 115, 117 in the tank 111, or by ay combustion thereof.

[0042] It has beem found that by applying an electric/electrostatic charge to the sludge which has been pumped to the tank 111 that this causes flocculation of the sludge, i.e. separation of nodules of solids which settle to the base of the settling tank, leaving a liquid at the upper end thereof. It is believed that the electric charge causes the fine solids to be attracted to one another so that they no longer remain in suspension within the sludge. The solids which settle to the bottom of the settling tank can then be withdrawn though an outlaw 133, whereas liquid can be withdrawn through a further oulet 135.

[0043] In the construction shown in FIG. 8, satisfactory separation of solids from liquids in a sludge mixture has been achieved without the use of a physical filter.

[0044]FIG. 9 shows a pump 205 similar to the pump 5 of FIG. 1 and having a drum 221 rotatable therein, similar to that shown in FIG. 2 and FIGS. 5 to 7. As in the embodiment of FIG. 1, the pump 205 generates a negative pressure in the same manner as the pump of FIG. 1, and it also has one or more puping tubes 207 entrained around the drum 221. The or each pumping tube 207 comprises a resiliently deformable external tube 209 within which a filter sleeve 211 is lcated. The intention is that as the sludge to be separated is pumped together the or each tube 207, so the solids within the sludge will be separated out from the liquids therein, as described above.

[0045]FIG. 10 shows a modication at the inlet end of the pumping and separating apparats. Instead of the inlet coupling member 237 being connected direct to the supply of sludge 201 to be pumped and separated, the sludge 201 is passed through a charging tank 249. The charging tank has two comparments 251 and 253 separated by a weir 255 which is removable. in tlw comparment 251 a pair of closely spaced electrodes 257,259 are provided which are conneced to a source of low voltage AC current, e.g. at about 12 volts.

[0046] In the compartment 253, a plurality of aeration pipes 261 are provided, each having at spaced intervals along their length a plurality of outlet nozzles 263 through which gentle jets of compressed air may exit into the base of the chamber 253. Located immediately above the air pipes 261 is at least one pair of rod-like electrodes 265, the electrodes of each pair being connected to a further source of low voltge AC electric current, e.g of 12 volts. These electrodes impart further electrical charge to the sludge before it enters the filter tube, thus assisting in the separation of solids from the liquid in the sludge.

[0047] It will be appreciated from the foregoing that in the various currents described electric or electrostatic charge has been imparted to the sludge to be separted by various different means. These various different means are not mutually exclusive and could be used either alone or togeter in any one or more of the the embodiments described. For example, in the embodiment of FIG. 8, the charging tank 249 could be located somewhere within the supply line 103.

[0048] Preferably, the strands of polypropylene 113 have a dielectric strength of about 100, as per the Altecs July 2000 trade catalogue.

[0049] It is preferred that the pump is rotated at a speed in the range of 30 to 110 r.p.m., preferably from 34.6 to 107 r.p.m. It may be rotated at a higher speed to generate the negative pressure at start up.

[0050] It will, of course, be understood that the present invention has been descibed above purely by way of example, and modifications of detail can be made within the scope of the invenion. It is envisaged, for example, that any type of pump could be used to pump the sludge/fluid mixture. 

1. A pumping apparatus for separating solids fromom liquids in a fluid mixture of solids and liquid, comprising a pump for pumping the fluid mixture from a supply thereof through a pipe into a settling tank, means to introduce an electrical charge into the fluid mixture whereby solids will precipitate from the fluid mixture in the settling tank.
 2. A peristaltic pumping apparatus comprising at least two fexible deformable tubes entrained around a cage, rotatable within a part arcuate casing and supporrng a plurality of rollers with push fluid through the tubes by squeezmg the tubes, a first one of the tubes having a first end held open to the intenor of the casing and an opposite end connected to a first outlet from the casing, whereby, upon operation of the apparatus, a pressure (hereinafter called negative pressure) which is less than that surrounding the casing will be generated with the casing, a second one of the tubes being connected at one end to an inlet in the casing, adapted to be connected to a fluid mixture of solids and liquids to be pumped and its opposite end being connected to a second outlet therein, whereby upon operation of the apparatus, the negative pressure will cause the second tube to move from a flattened state to a tubular state, whereby the fluid will be pumped though the second tube to the outlet, a settling tank, a pipe connecting the settling tank to the second outlet and means to introduce an elecical charge into the fluid mixture whereby solids will precipitate from the fluid in the settling tank.
 3. Apparatus according to claim 1 or 2 , wherein the means for generating an electrical or electrostatic charge within the fluid comprises a plurality of strands of polypropylene or the like located within a tube through which the fluid is pumped.
 4. Appartus according to claim 1 , wherein a receptor tank is provided for said fluid and said means for generating an electical charge comprises a pair of electrodes in the receptor tank for said fluid, said electrodes being connected to a source of low voltage AC current, and wherein said tank is earthed.
 5. Apparatus according to claim 2 , wherein the means for generating an elctrostatic charge within said fluid comprises a plurality of strands of polypropylene secured within said sccond tube.
 6. Apparatus according to claim 2 , whrein a receptor tank for said fluid and said means for generating an electical charge comprises a pair of electodes in the receptor tank for said fluid, said electrodes being connected to a source of low voltage AC current, and wherein said tank is earthed.
 7. Apparatus according to claim 3 , wherein a receptor tank is provided for said fluid and said means for generating an electrical charge comprises a pair of electrodes in the receptor tank for said fluid, said electrodes being connected to a source of low voltage AC current. and wherein said tank is earthed.
 8. Apparatus according to claim 1 , and including a tank through which at least part of said fluid is pumped, said tank incorporating an arcuate screen through which the fluid is forced by a plurality of brush heads having polypropylene bristles and supported on a rotor.
 9. Apparatus according to claim 2 , and including a tank through which at least part of said fluid is pumped, said tank incorporating an arcuate screen through which the fluid is forced by a plurality of brush heads having polypropylene bistles and supported on a rotor.
 10. Apparatus according to claim 3 , and including a tank through which at least part of said fluid is pumped, said tank incorporating an arcuate screen through which the fluid is forced by a plurality of brush heads having polypropylene bistles and supported on a rotor.
 11. Apparatus according to claim 5 , and including a tank through which at least part of said fluid is pumped, said tank incorporating an arcuate screen through which the fluid is forced by a plurality of brush heads having polypropylene bistles and supported on a rotor.
 12. Appartus for separating solids from liquids in a mixture of solids and liquids, comprising a closed casing having a side wall, at least part of which is arcuate, and a pair of spaced opposed end walls, connected by said part arcurate side wall, a cage rotatable within the casing, the cage having rollers spaced around its periphery, and a first resilient tube extending around the cage and located between the peripheries of the rollers and the internal surface of the arcuate side wall, one end of the first tube being connected to a first outlet in a wall of the casing and the opposite ned of the tube being connected to means within the casing to hold open said end of the tube, there being a non-return valve associated with the first tube, means to cause rotation of the cage such that air within the casing will be drawn into the held-open end of the tube and pumped along the tube in peristaltic manner to the outlet, the non-return valve preventing air from re-entering the tube, whereby the pressure within the casing is reduced, relative to that around the casing, at least one further resiliently deformable tube entrained over at least some of the rollers of the cage, so as to extend between the rollers and the arcuate part of the side wall of the casing, one end of said further tube being connected to a second outlet in a wall of the casing and an opposite end thereof being connected to an inlet in a wall of the casing, said inlet being adapted to be connected to said mixture, whereby rotation of the cage not only reduces the pressure within the casing to cause the at least one further tube to expand into a tubular state, but also pushes said mixture to be pumped along the further tube from the inlet to the outlet, and means to generate an electrical or electrostatic charge within said mixture to separate liquids fro solids in said mixture.
 13. Apparatus according to claim 12 , wherein a receptor tank is provided for said fluid and said means for generating a charge comprises a pair of electrodes in the receptor tank for said fluid, said electrodes being connected to a source of low voltage AC current, and wherein said tank is earthed.
 14. Apparatus according to claim 12 or 13 , wherein said means for generating a charge comprises a plurality of strands of polypropylene secured within said second tube.
 15. Apparatus according to claim 12 or 13 , and including a tank through which at least part of said fluid is pumped, said tank incorperating an arcuate screen which the fluid is forced by a plurality of brush heads having polypropylene bristles and supported on a rotor.
 16. Apparatus according to claim 14 , and including a tank through which at least part of said fluid is pumped, said tank incorperating an arcuate screen which the fluid is forced by a plurality of brush heads having polypropylene bristles and supported on a rotor.
 17. Apparatus according to claim 2 or claim 12 , wherein the cage supports a plurality of guides for the respective tubes, said guides being provided on a plurality of shafts circumferentially spaced around the cage.
 18. Apparatus according to claim 17 , wherein the shafts for guides are circumferentially spaced, around the cage, and separated by shafts carrying rollers.
 19. Apparatus according to claim 2 or claim 12 , wherein, on each guide shaft, three separate guides are provided, a central one being for the evacuating tube and located on either side thereof, there being a lateral guide for a respective pumping tube and wherein, on each roller shaft, thre is a central roller for the evacuating and spaced to either side thereof, a lateral roller for the respective pumping tubes. 